The present invention relates to a flame-retardant polyolefin-based rubber composition or, more particularly, to a polyolefin-based rubber composition imparted with excellent flame retardancy by the admixture of an organopolysiloxane.
Polyolefin-based synthetic rubbers in general are widely used as a material for electric insulation by virtue of their excellent electric and mechanical properties. A disadvantage in these synthetic rubbers is, however, their relatively high inflammability and, when they are once set on fire, the rubber sometimes is melted and drips to cause propagation of the flame. Therefore, it is a usual practice that a polyolefin-based rubber composition is formulated with various kinds of additives to be imparted with heat resistance and flame retardancy. In particular, a polyolefin-based rubber composition can be imparted with improved flame retardancy by formulating with a halogen compound and antimony oxide. The addition of these additives in large amounts is, however, accompanied by serious problems and disadvantages that the electric and mechanical properties of the rubber composition are adversely affected and, when a rubber composition admixed with these additives is set on fire, large volumes of toxic and corrosive gases are produced with little improvement in the phenomenon of dripping. Recently, it is proposed to formulate a polyolefin-based rubber composition with a large amount of aluminum hydroxide or magnesium hydroxide with an object to impart flame retardancy to the composition. This method of imparting flame retardancy, however, is not sufficiently effective unless the amount of the hydroxide is unduly increased while a rubber composition filled with such a large amount of the hydroxide has poor workability and the rubber article prepared of such a composition may have decreased mechanical strengths.